/Engine/Plugins/Protocols/MQTT/Source/MQTTCore/Public/IMQTTClient.h
Return true if the entire operation was successful (depends on QoS)
[TFuture](API\Runtime\Core\Async\TFuture)< bool > Publish ( const [FString](API\Runtime\Core\Containers\FString) & InTopic, const [TArray](API\Runtime\Core\Containers\TArray)< uint8 > & InPayload, [EMQTTQualityOfService](API\Plugins\MQTTCore\EMQTTQualityOfService) InQoS, const bool bInRetain )